Seagoing vessels are required in various types of offshore operations, including scientific surveys and oil and gas drilling and production. Such vessels are typically configured as drillships, barges and jack-up rigs, as well as supply and service ships.
Both active and passive techniques have been proposed for damping the natural oscillatory displacement of vessels to achieve roll and pitch stabilization in seas having periodic wave motion. Such techniques have utilized water tanks on the vessels and various arrangements of blowers, pumps, valves, valve actuators, roll and pitch sensors, and electronic control circuits for moving water in the tanks to counteract oscillatory roll and pitch motion. A common objective of heretofore known systems has been to make the natural frequency of oscillatory flow of water in the tanks approximately the same as the natural frequency of oscillations of the vessel, thereby to "tune" the tanks to the vessel. Once tuned, the damping action is achieved by causing the flow pattern of water in the tanks to be approximately 90.degree. out of phase with the natural oscillations of the vessel. The forces produced by the water in the tanks then tend to counteract the roll and pitch forces on the vessel.
Prior systems that attempt to achieve stabilization in the manner described above have the disadvantage that large counteracting, damping forces must be produced in order for the system to be effective. The equipment required to provide the large counteracting forces is complex and expensive. In active systems, high power blowers and pumps are typically required. Passive systems generally require high-capacity valves, special stabilizing tank configurations and control circuits for timing the flow of water in the tanks.